Known colloquially as ‘mad cow disease’, this is a fatal and untreatable disease. Along with scrapie in sheep and CREUTZFELDT-JAKOB DISEASE (CJD) in humans, BSE belongs to a class of unusual degenerative diseases of the brain known as transmissible spongiform encephalopathies. The disease is caused by abnormal PRION proteins, which are resistant to cellular degradation. These accumulate in, and eventually cause the death of, nerve cells both in the spinal cord and the brain. The appearance of BSE in cattle is believed to have been caused by a gene mutation (see GENETIC DISORDERS) although whether this mutation first occurred in cattle or in some other animal remains uncertain. Although the first case of BSE in the UK was officially reported in 1985, the first cattle are thought to have been infected in the 1970s. BSE spread to epidemic proportions because cattle were fed meat and bone meal made from the offal of cattle suffering from or incubating the disease. Mother-to-calf transfer is another likely route of transmission, although meat and bone meal in cattle feed were the main cause of the epidemic. The epidemic reached its peak in 1992 when the incidence of newly diagnosed cases in cattle was 37,545.

Since the BSE epidemic in cattle developed in the UK in the 1980s, a new variant of the rare brain disease CREUTZFELDT-JAKOB DISEASE (CJD) has been identified and is believed to be the result of consumption of the meat of BSE-infected cattle. The new variant has affected younger people and may have a shorter incubation period. If this incubation period turns out to be the same as for the other types of CJD, however, the peak of this outbreak may not have been reached. There had been 177 reported cases in the UK by 2016.

Although initially thought to be a problem primarily confined to the UK, several other countries – notably France, Germany, Spain, Switzerland and the United States – have also discovered BSE in cattle.